Communication devices, whether handheld or not, are known to have varying capabilities, enabling different levels of support for large multimedia services, applications, and IP-based wireless and wired connectivity. Users of handheld devices can move within a wireless domain and enjoy spatial mobility while using multimedia services. However, handheld devices are still limited in term of autonomy, display capacity, ease of use and computational power. Stationary devices, like PC or wire-line IP-Phones, continue to be more adapted for multimedia services, but not spatial mobility.
Enabling service transitions between all available user-devices allows one to take advantage of the capabilities offered by different types of devices. Service transfer between different communicating devices can be supported by ensuring some mobility in the application-session layer. Solutions exist to enable session mobility between multimedia applications within two-party communication. In the case of multiparty communications, moving a session from one device to another device is more complex. In some cases other participants in the communication are affected, which makes the procedure burdensome. For example, in situations where users join the conference or leave it, the transferred session host needs to be informed about such events and conference coherence has to be maintained.
Several approaches and topologies have been proposed for distributed Internet multiparty communication. Some of them are centralized approaches using a conference server that carries out signaling/media-mixing between participants. One centralized approach aims to enable one participant of a two-party communication to invite other users and to ensure media mixing and conference signaling. A second centralized approach intends to dedicate conference media mixing and/or session signaling management to a central third-party machine. The major drawback of these two approaches is that as soon as the central element leaves the conference, there is no way for remaining participants to continue conferencing. Some decentralized approaches use the multicast techniques to create network links between participants. This model is based on the IP multicast technique where each active participant should use multicast addresses that contain the addresses of participants to join. Over and above overloading networks, this approach requires routers to be multicast-enabled. Therefore, deploying multicast conferences outside local networks is not conceivable.
Therefore, there is a need for a new model that will allow session mobility in multiparty communication environments.